<article id="wikiArticle">
<div></div>
<p>内置的<strong><code>Symbol.isConcatSpreadable</code></strong><code>符号用于配置某对象作为</code><a href="Reference/Global_Objects/Array/concat" title="concat() 方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。"><code>Array.prototype.concat()</code></a>方法的参数时是否展开其数组元素。</p>
<div><table class="standard-table">
<thead>
<tr>
<th class="header" colspan="2"><code>Symbol.isConcatSpreadable</code> 属性的属性特性：</th>
</tr>
</thead>
<tbody>
<tr>
<td>writable</td>
<td>false</td>
</tr>
<tr>
<td>enumerable</td>
<td>false</td>
</tr>
<tr>
<td>configurable</td>
<td>false</td>
</tr>
</tbody>
</table></div>
<h2 id="描述">描述</h2>
<p><code>@@isConcatSpreadable</code> 符号 (<code>Symbol.isConcatSpreadable</code>) 可以直接定义为对象属性或继承而来，它是布尔类型。它可以控制数组或类似数组（array-like）的对象的行为：</p>
<ul>
<li>对于数组对象，默认情况下，用于concat时，会按数组元素展开然后进行连接（数组元素作为新数组的元素）。重置<code>Symbol.isConcatSpreadable</code>可以改变默认行为。</li>
<li>对于类似数组的对象，用于concat时，该对象整体作为新数组的元素，重置<code>Symbol.isConcatSpreadable</code>可改变默认行为。</li>
</ul>
<h2 id="示例">示例</h2>
<h3 id="数组">数组</h3>
<p>默认情况下，<a href="Reference/Global_Objects/Array/concat" title="concat() 方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。"><code>Array.prototype.concat()</code></a> 展开其元素连接到结果中：</p>
<pre><code  class="language-javascript">var alpha = ['a', 'b', 'c'], 
    numeric = [1, 2, 3]; 

var alphaNumeric = alpha.concat(numeric); 

console.log(alphaNumeric); // 结果: ['a', 'b', 'c', 1, 2, 3]
</code></pre>
<p>设置<code>Symbol.isConcatSpreadable</code>为<code>false</code>：</p>
<pre><code  class="language-javascript">var alpha = ['a', 'b', 'c'], 
    numeric = [1, 2, 3]; 

numeric[Symbol.isConcatSpreadable] = false;
var alphaNumeric = alpha.concat(numeric); 

console.log(alphaNumeric); // 结果: ['a', 'b', 'c', [1, 2, 3] ]
</code></pre>
<h3 id="Array-like_对象">Array-like 对象</h3>
<p>对于类数组 (array-like)对象，默认不展开。期望展开其元素用于连接，需要设置 <code>Symbol.isConcatSpreadable</code> 为true：</p>
<pre><code  class="language-javascript">var x = [1, 2, 3];

var fakeArray = { 
  [Symbol.isConcatSpreadable]: true, 
  length: 2, 
  0: "hello", 
  1: "world" 
}

x.concat(fakeArray); // [1, 2, 3, "hello", "world"]
</code></pre>
<h2 id="技术标准">技术标准</h2>
<table class="standard-table">
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<tr>
<th scope="col">标准</th>
<th scope="col">状态</th>
<th scope="col">备注</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-symbol.isconcatspreadable" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Symbol.isconcatspreadable</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-symbol.isconcatspreadable" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Symbol.isconcatspreadable</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td>No change.</td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div><p></p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td><a href="/en-US/Firefox/Releases/48" title="Released on 2016-08-02.">48</a> (48)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>48.0 (48)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
</tr>
</tbody>
</table>
</div>
<h2 id="参考">参考</h2>
<ul>
<li><a href="Reference/Global_Objects/Array/concat" title="concat() 方法用于合并两个或多个数组。此方法不会更改现有数组，而是返回一个新数组。"><code>Array.prototype.concat()</code></a></li>
</ul>
</article>